Advanced Editing (Learning the vi Editor, Sixth Edition)

This chapter introduces you to some of the more advanced capabilities of the vi and ex editors. You should be reasonably familiar with the material presented in the earlier chapters of this book before you start working with the concepts presented in this chapter.

This chapter is divided into five parts. The first part discusses a number of ways to set options that allow you to customize your editing environment. You'll learn how to use the set command and how to create a number of different editing environments using .exrc files.

The second part discusses how you can execute UNIX commands from within vi, and how you can use vi to filter text through UNIX commands.

The third part discusses various ways to save long sequences of commands by reducing them to abbreviations, or even to commands that use only one keystroke (this is called mapping keys). It also includes a section on @-functions, which allow you to store command sequences in a buffer.

The fourth part discusses the use of ex scripts from the UNIX command line or from within shell scripts. Scripting provides a powerful way to make repetitive edits.

The fifth part discusses some features of vi that are especially useful to programmers. vi has options that control line indentation and an option to display invisible characters (specifically tabs and newlines). There are search commands that are useful with program code blocks or with C functions.

7.1. Customizing vi

You have seen that vi operates differently on various terminals. (For instance, on "dumb" terminals, vi inserts @ symbols in place of deleted lines; on intelligent terminals, vi redraws the screen with each edit.) On modern UNIX systems, vi gets operating instructions about your terminal type from the terminfo terminal database. (On older systems, vi uses the original termcap database.)[27]

[27]The location of these two databases varies from vendor to vendor. Try the commands man terminfo and man termcap to get more information about your specific system.

There are also a number of options that you can set from within vi that affect how it operates. For example, you can set a right margin that will cause vi to wrap lines automatically, so you don't need to hit RETURN.

You can change options from within vi by using the ex command :set. In addition, whenever vi is started up, it reads a file in your home directory called .exrc for further operating instructions. By placing :set commands in this file, you can modify the way vi acts whenever you use it.

You can also set up .exrc files in local directories to initialize various options that you want to use in different environments. For example, you might define one set of options for editing English text, but another set for editing source programs. The .exrc file in your home directory will be executed first, then the one in your current directory.

Finally, any commands stored in the shell variable EXINIT will be executed by vi on startup. The settings in EXINIT take precedence over those in the home directory .exrc file.

7.1.1. The :set Command

There are two types of options that can be changed with the :set command: toggle options, which are either on or off, and options that take a numeric or string value (such as the location of a margin or the name of a file).

Toggle options may be on or off by default. To turn a toggle option on, the command is:

:set option

To turn a toggle option off, the command is:

:set nooption

For example, to specify that pattern searches should ignore case, type:

:set ic

If you want vi to return to being case-sensitive in searches, give the command:

:set noic

Some options have a value assigned to them. For example, the window option sets the number of lines shown in the screen's "window." You set values for these options with an equal sign (=):

:set window=20

During a vi session, you can check which options vi is using. The command:

:set all

displays the complete list of options, including options that you have set and defaults that vi has "chosen." The display should look something like this:[28]

[28]The result of :set all depends very much on the version of vi you have. This is typical of UNIX vi; what comes out of the various clones will be different.

autoindent         nomodelines                       noshowmode
autoprint          nonumber                          noslowopen
noautowrite        nonovice                          tabstop=8
beautify           nooptimize                        taglength=0
directory=/var/tmp paragraphs=IPLPPPQPP LIpplpipnpbp tags=tags /usr/lib/tags
noedcompatible     prompt                            tagstack
errorbells         noreadonly                        term=vt102
noexrc             redraw                            noterse
flash              remap                             timeout
hardtabs=8         report=3                          ttytype=vt102
noignorecase       scroll=11                         warn
nolisp             sections=NHSHH HUuhsh+c           window=23
nolist             shell=/bin/ksh                    wrapscan
magic              shiftwidth=8                      wrapmargin=0
nomesg             showmatch                         nowriteany

You can find out the current value of any individual option by name, using the command:

:set option?

The command:

:set

shows options that you have specifically changed, or set, either in your .exrc file or during the current session.

For example, the display might look like this:

number sect=AhBhChDh window=20 wrapmargin=10

7.1.2. The .exrc File

The .exrc file that controls your own vi environment is in your home directory (the directory you are in when you first log on). You can modify the .exrc file with the vi editor, just as you can any other text file.

If you don't yet have an .exrc file, simply use vi to create one. Enter into this file the set, ab, and map commands that you want to have in effect whenever you use vi or ex. (ab and map are discussed later in this chapter.) A sample .exrc file might look like this:

set nowrapscan wrapmargin=7
set sections=SeAhBhChDh nomesg
map q :w^M:n^M
map v dwElp
ab ORA O'Reilly & Associates, Inc.

Since the file is actually read by ex before it enters visual mode (vi), commands in .exrc need not have a preceding colon.

7.1.3. Alternate Environments

In addition to reading the .exrc file in your home directory, you can allow vi to read a file called .exrc in the current directory. This allows you to set options that are appropriate to a particular project.

For example, you might want to have one set of options in a directory mainly used for programming:

set number autoindent sw=4 terse
set tags=/usr/lib/tags

and another set of options in a directory used for text editing:

set wrapmargin=15 ignorecase

Note that you can set certain options in the .exrc file in your home directory and unset them in a local directory.

You can also define alternate vi environments by saving option settings in a file other than .exrc and reading in that file with the :so command. (so is short for source.)

For example:

:so .progoptions

Local .exrc files are also useful for defining abbreviations and key mappings (described later in this chapter). When we write a book or manual, we save all abbreviations to be used in that book in an .exrc file in the directory in which the book is being created.

NOTE: In all modern versions of vi, you have to first set the exrc option in your home directory's .exrc file before vi will read the .exrc file in the current directory:

set exrc

This mechanism prevents other people from placing, in your working directory, an .exrc file whose commands might jeopardize the security of your system.[29]

[29]The original versions of vi automatically read both files, if they existed. The exrc option closes a potential security hole.

7.1.4. Some Useful Options

As you can see when you type :set all, there are an awful lot of options that can be set. Many of them are used internally by vi and aren't usually changed. Others are important in certain cases, but not in others (for example, noredraw and window can be useful on a dialup line at a low baud rate). The table in Section 3.1 contains a brief description of each option. We recommend that you take some time to play with setting options—if an option looks interesting, try setting it (or unsetting it) and watch what happens while you edit. You may find some surprisingly useful tools.

As discussed earlier in this book, one option, wrapmargin, is essential for editing non-program text. wrapmargin specifies the size of the right margin that will be used to autowrap text as you type. (This saves manually typing carriage returns.) A typical value is 7 to 15:

:set wrapmargin=10

Three other options control how vi acts when conducting a search. Normally, a search differentiates between uppercase and lowercase (foo does not match Foo), wraps around to the beginning of the file (meaning that you can begin your search anywhere in the file and still find all occurrences), and recognizes wildcard characters when pattern matching. The default settings that control these options are noignorecase, wrapscan, and magic, respectively. To change any of these defaults, you would set the opposite toggle options: ignorecase, nowrapscan, and nomagic.

Options that may be of particular interest to programmers include: autoindent, showmatch, tabstop, shiftwidth, number, and list, as well as their opposite toggle options.

Finally, consider using the autowrite option. When set, vi will automatically write out the contents of a changed buffer when you issue the :n (next) command to move to the next file to be edited, and before running a shell command with :!.

Chapter 7. Advanced Editing

Contents:

7.1. Customizing vi

7.1.1. The :set Command

7.1.2. The .exrc File

7.1.3. Alternate Environments

7.1.4. Some Useful Options